Various types of organic compounds have been used to advantageously alter certain properties of wet hydraulic binder compositions. One class of components, which can collectively be called “superplasticizers”, fluidify or plasticize wet cement composition to obtain a more fluid composition. A controlled fluidity is desired, such that the aggregate used in mortars and concretes does not segregate from the cement paste. Superplasticizers may also allow the cement composition to be prepared using a lower water to cement ratio in order to obtain a composition having a desired consistency which often leads to a hardened cement composition having a higher compressive strength development after setting.
A good superplasticizer should not only fluidify the wet hydraulic binder composition to which it is added, but also maintain the level of fluidity over a desired period of time. This time should be long enough to keep the wet composition fluid, e. g. in a ready-mix truck, while it is on its way to a job site. Another important aspect relates to the period for discharging the truck at the job site and the period needed for the cement composition for being worked in the desired final form. On the other hand, the cement mixture cannot remain fluid for a too long time period such that the set is greatly retarded, because this will slow down the work on the job and show negative influences on the characteristics of the final hardened products.
Conventional examples of superplasticizers are melamine sulfonate/formaldehyde condensation products, naphthalene sulfonate/formaldehyde condensation products and lignosulfonates, polysaccharides, hydroxycarboxylic acids and their salts and carbohydrates.
In most cases, superplasticizer are multi-component products with copolymers based on polyalkylene glycol monovinyl ethers and unsaturated dicarboxylic acid-derivatives as most important species. The European Patent EP 0 736 553 B1 discloses such copolymers comprising at least three sub-units and especially one unsaturated dicarboxylic acid derivative, polyalkylene glycol monovinyl ethers and additionally one hydrophobic structural unit, such as ester units. The third structural unit can also be represented by polypropylenoxid- and polypropylenoxid-polyethylenoxid-derivatives, respectively.
The German published application DE 195 43 304 A1 discloses an additive for water containing mixtures for the construction field comprising a) a water-soluble sulfonic acid-, carboxylic- or sulfate group containing cellulose derivative, b) a sulfonic acid- and/or carboxylic acid containing vinyl-(co)-polymer and/or a condensation product based on aminoplast-builders or acryl containing compounds and formaldehyde. This additive shall show sufficient water retention ability and rheology-modifying properties. Therefore, this additive shall be suitable for construction chemical compositions containing cement, plaster of pads, lime, anhydrite and other hydraulic binder components.
Copolymers based on unsaturated monocarboxylic or dicarboxylic acid derivatives, oxyalkylenglycolalkenylethers, vinylic polyalkylenglykol, polysiloxane or ester compounds used as additives for aqueous suspensions based on mineral or bituminous binders are described in U.S. Pat. No. 6,777,517 B1. The use of such additives results in a decrease in the water/binder ratio and leads to highly fluid building materials without segregation of individual constituents from the building material mixture. The copolymers according to the U.S. '517 patent are useful as additives for aqueous suspensions of inorganic and organic solids and especially for suspensions that are based on mineral or bituminous binders such as cement, plaster of Paris, lime, anhydrite or other building materials based on calcium sulfate.
Also disclosed are copolymers of unsaturated ethers that can be used as plasticizers for cement containing mixtures, such as described in EP 0 537 870 A1. These copolymers contain an ether co-monomer and as additional co-monomer an olefinic unsaturated mono-carboxylic acid or an ester or a salt thereof, or alternatively an olefinic unsaturated sulfonic acid. These copolymers have a very short ether side chain of from 1 to 50 units. The short side chain causes a sufficient plasticizing effect of the copolymers in cement containing masses with a reduced slump loss of the construction chemicals mass itself.
U.S. Pat. No. 6,139,623 discloses an emulsion admixture for use in hydraulic cement compositions formed by emulsifying an antifoaming agent, a surfactant and a copolymer having a carbon-containing backbone to which are attached groups that function as cement-anchoring members by forming ionic bonds and oxyalkylene groups. This admixture comprising an ethylene oxide/propylene oxide (EO/PO) type comb polymer and an antifoaming agent allows a predictable air control in hydraulic cement compositions such as concrete. The term “cement composition” refers to pastes, mortars, grouts such as oil well cementing grouts, and concrete compositions comprising a hydraulic cement binder. Typical antifoaming agents are phosphate ester, borate ester and polyoxyalkylene copolymers with defoaming properties. The surface active component (surfactant) is said to stabilize the emulsion mixture and is chosen from the group consisting of an esterified fatty acid ester of a carbohydrate, a C2 to C20 alcohol having polyoxyalkylene groups or a mixture thereof.
An admixture composition for cementitious compositions is published in US 2005/0257720 A1. This admixture comprises a water insoluble defoamer, an amine salt solubilizing agent capable of solubilizing the water insoluble defoamer in an acidic medium, and optionally a dispersant for cementitious compositions. This combination of an amine salt solubilizing agent, a water insoluble defoamer and a dispersant provides a stable admixture for cementitious compositions by showing a long-term storage stability. Polycarboxylates are typical dispersant components. Mineral oils, vegetable oils, fatty acid ester, ether compounds, hydroxyl functional compounds, an alcohol, a phosphoric ester, a silicon, a polyoxyalkylene, a hydrocarbon, an acetylenic compound and a polymer comprising at least one of propylene oxide or ethylene oxide moieties are typical water insoluble defoamer. Hydraulic cements are portland cement, masonry cement, alumina cement, refractory cement, magnesia cement, calciumsulfoaluminate cement and oil well cements.
WO 2006/021792 A2 discloses a method of cementing in a subterranean formation whereby a cement composition is provided that comprises water, hydraulic cement and a defoamer. Components of the defoamer include at least one compound selected from the group of a defoaming hydrocarbon base fluid, a surfactant, a hydrophobic particle or a mixture therefore. The hydraulic cement can be a gypsum cement and the cement composition can further contain a dispersant.
As indicated above this application is based on the prior patent published as US 2006/0281886, which discloses a co-polymer comprising two monomer components with a component a) being an olefinic unsaturated monocarboxylic acid co-monomer or an ester or a salt thereof or an olefinic unsaturated sulfuric acid co-monomer or a salt thereof, and with component b) preferably represented by an ether compound. This two monomeric co-polymer can be preferably used as a superplasticizer in a hydraulic binder containing composition. There it is alternatively disclosed that the co-polymer can be used in combination with a defoaming component that is also an additional structural unit of the co-polymer. Consequently, the defoaming component can be chemically attached to the co-polymer or being present in free form in a blend. Under general aspects the prior art teaches the use of dispersing agents (plasticizers) such as polycarboxylate ethers (PCE) as typical additive for calcium sulfate containing binder systems. This results in a water reduction as well as in an enhancement of physical properties such as compressive strength due to an increase in gypsum cast density. Additionally, the workability and preferably the rheological behavior of the construction chemicals composition are improved. On the other hand the addition of PCE based dispersants causes a distinct air entrainment to the binder component that worsens the physical properties of the composition. For overcoming these drawbacks defoamer components are used as additional additive to the dispersing agent. However, defoamers show a low solubility in aqueous formulations and cause an insufficient stability. Moreover, the defoaming properties of the formulation decrease over time due to the resulting phase separation of the defoamer and the dispersant.
Based on the different characteristics and the availability of the superplasticizers mentioned above, it has been further desired to come up with new admixtures which are an improvement over the current state of the art. It is thus an object of this invention to provide new additives for calcium sulfate binder containing compositions which impart to wet binder compositions excellent fluidizing and water reduction properties. An additional aspect is an aqueous and calcium sulfate based suspension with sufficient workability.